The present invention is apparatus for enhancing an observers ability to see clearly an illuminated area in a partially transparent medium, by reducing the amount and effect of scattered light from illuminated particles in the medium. It is useful in fog, smoke and underwater.
The effect on an observer's visual perception of scatter from illuminated particles is well known to persons who have driven working underwater with portable search lights. Light from the illumination supplied to light up the field of interest in front of the observer is reflected back into the observers eyes and dazzles him, reduces the apparent contrast of details in the scene, reduces his "dark adaption" and generally destroys or inhibits his visual perception.
One known system for reducing the effect of scattered light is range gating in which the illumination is pulsed and a shutter in front of the observer is opened at intervals coinciding with the time at which illumination from the scene to be viewed reaches the observers eyes. However, this system requires relatively complex equipment and is expensive.
It is also customary practice in underwater work to separate the light source from the observer to the greatest extent possible. This eliminates illumination of particles close to the observer and reduces the amount of light scattered back to the observer to some extent, but there is still sufficient light scattered from particles in the foreground to severely restrict the observers perception of the scene.